Recovery of olefins from c7 to c9 corresponding olefin-paraffin mixtures



April 30, 1963 J. s. BURCH RECOVERY OF OLEFINS FROM'C7TO C 9 CORRESPONDING OLEFIN-PARAFFIN MIXTURES Filed Dec. 9, 1960 2 m R 0 m NE 4 M W ww nw 3 E EE v m mm A MR R 0 4 V 0 J: W 4 9 m 4 IFW zo m um 5 n/ 6 o m w E 5 a II-m UZ Q IuQ 0 2 A 2 2 N U N WHO 2 HQ FFE IA fin mm l.|v 0A TT P. ES c A A 4 United States Patent 3,087,866 RECOVERY OF OLEFINS FROM 0; T0 C CORRE- SPONDING OLEFIN-PARAFFIN MIXTURES John S. Burch, Dickinson, Tex., assignor to Union Carbide Corporation, a corporation of New York Filed Dec. 9, 1960, Ser. No. 75,462 3 Claims. (Cl. 202-42) This invention rel-ates to the separation of olefinparaffin mixtures wherein the constituents contain from seven to nine carbon atoms, and particularly to the recovcry of olefin rich fractions from such hydrocarbon mixtures. Still more particularly, the invention relates to the separation and recovery of relatively high boiling isomeric olefins trom mixtures of their corresponding isomeric parafiins by azeotropic distillation. While the process of the present invention is applicable to any mixture of an olefin and its corresponding paraflin, provided it contains trom 7 to 9 carbon atoms, the mixtures herein shown are by-product hydrocarbon fractions of the well known Oxo Process. This is merely illustrative and not intended in any way to limit or restrict this invention. The present invention is applicable to any corresponding paraffin-olefin mixtures of hydrocarbons having from 7 to 9 carbon atoms, regardless of the source of the mixture.

Distillation of the products trom the hydrotormylation of olefins yields a head fraction containing a mixture of the olefin, its corresponding parafiin and aldehydes. This occurs in the well known Oxo Process wherein olefinic hydrocarbons are reacted with carbon monoxide and hydrogen to produce an aldehyde-alcohol mixture. A portion of the olefin raw material passes through the converter unreacted and. is removed with the aldehyde-alcohol in the mixed product stream. Another portion of the olefin raw material is hydrogenated to the corresponding saturated hydrocarbon by a side reaction in the converter. The unreacted ole-fin and the by-product parafiin, some cat the aldehyde and water are removed as a heads traction on distillation of the converter product. This mixed hydrocarbon fraction generally contains 50 to 55 percent of the unreacted olefin, a concentration too low -for economic recycling to the converter. Resolution between the olefinic and paraffinic hydrocarbons cannot be made by fractional distillation because each is a mixture of isomers of overlapping volatilities. The usual methods of separation employed, such as extractive distillation, solvent extraction and adsorption, are either inoperable, economically prohibitive or of poor efiiciency when olefi-ns of seven or more carbons are involved.

The present invention provides a means of separating the unreacted olefin from this mixture through the use of a relatively small quantity of a moderately priced en- 1 trainer, said entrainer being recycled with little make-up required, and is adaptable to simple conventional carbon steel equipment. The olefin fraction so obtained can be readmitted to the 0x0 Process without further treatment.

The preferred form of the invention involves its application to a continuous process and the use of acetonitrile as the entrainer. The preferred form is illustrated in the FIGURE.

Referring to the figure, the olefinic-parafiinic hydrocarbon mixture is fed from storage tank 1 through line 2 to the side of the dehydrating still '3. The base of this continuous column is heated conventionally, resulting in the removal of the hydrocarbon-water azeotropes through vapor line 4 and condenser 5 to decanter 7. After phase separation, the Water layer is removed through line 8 and the upper hydrocarbon layer is returned as reflux through line 9 to dehydrating still 3. The dehydrated hydrocarbons atcrernoved from the base of the still through line 3,087,866 Patented Apr. 30, 1963 10 and are fed through line 10 to separation still 11. In

this column, the hydrocarbon mixture is contacted With acetonitrile, which had previously been pumped into the column from acetonitrile storage tank 20 through lines 21 and 10. The more volatile paralfin acetonitr-ile azeotropes are removed from the top of the column through vapor line 1 2 and are condensed in condenser 13. The condensate there flows through line 14 into decanter 15, where it separates into an upper hydrocarbon-rich phase and a lower acetonitrile-rich phase. The upper layer is withdrawn from the system through line 16 to receiver tank 22 and the lower acetonitrile layer is returned as reflux to column 11 through line 1-8. To maintain proper reflux on the column, a portion of the upper layer may also be returned to the column through line 24.

The amount of acetonitrile in the column is limited to the extent that a separation between the acetonitrilehydrocarbon azeotropes and the concentrated olefins is effected in the lower trays, and the concentrated olefins, containing little or no acetonitrile, are removed through line 19 firom the base of the column and collected in receiver tank 23. To compensate for minor losses of acetonitrile by partial solution in the upper layer of decanter =15, acetonitrile may be added intermittently from storage tank 20 through lines 21 and 10. In case of incomplete water removal in dehydrating still 3, a slow bleed of acetonitrile-water mixture can be taken from the lower layer of decanter 15 through line 17 to maintain anhydrous conditions in column 111.

The invention can also be applied to a batchwise technique. In this case, a mixture of the acetonitrile and the olefin-paraffin mixture is charged to the kettle of a batch still. The overhead product from the column is condensed and the liquid phases separated in a decanter. The lower acetonitrile layer is returned to the column as reflux, together with sufficient upper layer to maintain proper reflux on the system. A stream from the upper layer, consisting of a concentrate of the paraffinic hydrocarbons, is also withdrawn to the product tank. When separation of the parafiinic component by this method is essentially complete, the reflux and product system is changed so that all the upper layer is returned as reflux to the column and all of the lower layer is withdrawn to a second product tank. When the acetonitrile has been stripped from the system in this manner, the still can be shut down and the kettle liquid, consisting of enriched olefins suitable for recycling to the Oxo Process, can be pumped from the system. The acetonitrile solvent, in the second product tank, can then be returned to the system for reuse with the next batch.

Acetonitrile can also be used as the aqueous azeotrope, containing 81.5 percent acetonitrile at the expense of some of the separation etficiency. Usage of this azeotrope would obviate the need of dehydrating still 3 in the figure, and would permit the base of separation column 11 to operate at a lower temperature.

The following specific examples will serve to further illustrate the present invention and are not to be construed as limiting the present invention.

EXAMPLE 1 A mixture of 200 milliliters recovered C hydrocarbon (41 percent nonane, 54 percent. nonene and 5 percent decanal) and milliliters of acetonitrile (containing 0.25 percent water) was fractionally distilled through a 30-tray Oldershaw column. The distillate was condensed and the lower (acetonitrile) layer was returned to the column. Distilled fractions and the residue were analyzed for the components, and the results are reported in Table I.

Table I Composition, vol. percent, CHsCN free Vol.

basis percent Head nonenes, Fraction temp., CHHCN 0. Percent Aldehyde and of total Nonanes Nonenes as aldehyde Cg charge decanal tree basis 1 55 7.5 77 18 4.9 19 2 c5 05 7.5 76 24 0.4 24 2A (lower layer). 66 77 Nil 3 77 78 7.5 so 20 Nil 20 4. 78 7.5 67 32 0.7 32 5 78 7.5 40 0.4 40 5.. 7s -7s.5 7.5 64 34 1.9 35 7 78. 7. 5 45 55 0. 4 55 8 78.579 7.0 40 50 0.7 50 9 7.0 31 67 1.9 as Col.hold-up(ealc. 5.5 78 1.9 80 Residue 28.0 8 73 19. 2 90 Considering fractions 1 through 6 as the waste nonane 20 Tabl IV fraction and fractions 7 through 9 plus the column holdup and residue as the recovered nonene fraction, a disv0 oieontained component, Percent tribution of the components of the sample appears in ill r z Table II. 5. 3 Table II Aldehyde ornoN Nonanes Nonenes as free basis decanal Vol. of contained component, Percent Hummers fif gi if Waste nonane fraction. 57. 2 4s. 5 0. a 42 and Recovered nonene lractio 19.2 54. 9 9.8 74 Aldehyde CInCN Nonanes Nonenes as free basis Total 103'4 decanal A recovery of 53 percent of the contained nonenes, in Waste nonane fraction 63.6 26. 2 1. 2 29 Recovered nonene fractionm 4 75 4 1L 4 76 a fraction of 74 percent pur ty (on an aldehyde and ace tonitrile free basis), was achieved. The recovered nonene Tta1 10115 fraction also contained 97 percent of the aldehydes A recovery of 74 percent of the contained nonenes, in a fraction of 76 percent purity (on an aldehyde and acetonitrile free basis), was achieved. The recovered nonene fraction also contained 91 percent of the aldehydes present in the original sample.

EXAMPLE 2 present in the original sample.

EXAMPLE 3 A nonene-nonane mixture (48 percent nonane, 51 percent nonene and 1 percent decanal) was separated into nonene-rich and nonene-lean fractions by continuous azeotropic distillation with acetonitrile. The crude hydrocarbon mixture was introduced at the side of a continuous column at a point approximately equidistant from the top and bottom of the packed section. The column contained a limited amount of acetonitrile, so that there was a sharp temperature gradient in the lower sections of the column, and the product stream from the base of the column contained no acetonitrile. The overhead stream from the column was condensed, and the liquid layers separated. The lower (acetonitrile) layer and a portion Table III Composition, vol. percent, CH;ON tree .3 Vol.

basis percent Head nonenes, Fraction 301119., CH3CN 0. Percent Aldehyde and of total Nonanes Nonenes as aldehyde C9 charge decanal free basis 1 7. 0 66 31. 5 2. 5 32 1A (lower layer) 2 7. 0 62 38 Nil 38 7. 5 59 41 Nil 41 6. 5 58 42 Nil 42 7. 5 58 42 N 11 42 7. 5 53 47 Nil 47 7. 5 54 46 N11 46 7. 5 54 46 N11 46 7. 5 45 55 0. 4 55 C01. hold-up (calm) 7. 0 30 0. 4 70 Residue 27. 5 15 67 17. 6 82 Considering fractions 1 through 8 as the waste nonane fraction and fraction 9 plus the column hold-up and residue as the recovered nonene fraction, a distribution of the components of the sample is provided in Table IV.

of the upper (hydrocarbon) layer were returned to the column as reflux. The remainder of the upper layer was collected as overhead product. The column was operated so that the overhead product and the base product streams 3,087,866 51 6 were removed at the same rate. Make-up acetonitrile and residue as the recovered nonene fraction, a distribuwas added occasionally to the feed. Summarizing: tion of the components of the sample is collected in Overhead product: Grams Table Table VI Nonanes 2,166 Nonenes 1,07 1

Vol. of contained component Percent Aldehydes, as decanal 22 milliliters nonenes, aldehyde and Total 3,259 Aldehyde onto; Nonanes Nonenes as free basis dceanal Base Product:

Waste nonane fraction 202. 1 90.0 1. 9 31 Nonanes 887 Recovered nonene fraction... 94. 9 277. 5 33. 6 75 Nonenes 2,547 Aldehyde, as decanal 53 Total 297-0 367-5 Total 3 487 A 200 milliliter portion of the waste nonane fraction (69 percent nonane, 30.6 percent nonene and 0.4 percent dacanal) was then mixed with 50 milliliters of aceto- 1 c a Total recovery" 6746 nitrile and distilled through the same column n the same 1 99 Percent manner as in the initial distillation. Analyses of the re- The base product stream contained 70.4 percent of the sulting fractions is collected in Table V Table VII Composition, vol. percent, CHzCN tree Vol.

basis percent Head nonenes, Fraction temp, CH CN 0. Percent Aldehyde and of total Nonanes Nonenes as aldehyde C9 charge decanal tree basis 1 77.0-77.9 11.7 84 16 0.4 16 2.-. 77. 9-78. 0 12. 2 7s 22 Nil 22 a 78.0 12.2 75 25 Nil 25 4.-- 7s. 0 12. 2 73 26 0. 7 26 5 78.0-78.2 12. 5 72 2s Nil 28 7s. 2 12. 5 72 27 0. 7 27 78.2 7.5 64 36 Nil :36 0.7 55 45 Nil 45 Residue 18.5 45 54 0.9 55

nonenes present in the original sample, and had a nonene Considering all the distilled fractions and the column hold-up as a waste nonane fraction and the residue as a recovered nonene fraction, a distribution of the components is collected in Table VIII, when calculated on the basis of the entire nonane fraction from the previous distillation (294 milliliters).

stripping from the column at the end of the run. The

remaining 101 grams of acetonitrile left the system with Table the overhead product, from which it can be recovered either by subsequent distillation of this stream or by gffifig gg extraction with water. a hga 8.11 EXAMPLE 4 Aldehyde ornoN Nonanes Nonenes as freebasls A mixture of 700 milliliters recovered C hydrocarbon decanal (41 percent nonane, 54 percent nonene and 5 percent W aste nonane fraction 178.2 60.8 0.7 25 decanal) and 50 milliliters aceton trile (containing 0.25 Recovered nonene fraction 2 2H 0.5 55 percent water) was fractionally distilled through a SO-tray Oldershaw column. The distillate was condensed and 55 Tml 1 2 the lower (acetonitrile) layer was returned to the column. Distilled fractions and the residue were analyzed for the components and the results are collected in Table V.

The nonene recoveries and the purities of the nonene fractions are shown in Table IX for the initial distillation Considering fractions 1 through 4 as waste nonene fraction and fractions 5 through 6 plus the column hold-up singly and for the combined initial distillaton and subsequent redistillation of the nonane fraction.

Table IX Table XI Initial Redistil- Com- Vol. 01' contained distillation bined components, milli- Percent lation of nonane distilliters heptenes fraction laticn 5 CIIQON free basis Heptanes Heptenes N onene recovery, vol. percent 75. 5 8.0 83. 5 N onene purity, v01. percent of recovered nouenc fraction, aldehyde and Waste heptane tract-ion 217.9 70.1 24 CHaCN free basis 75 55 70 Recovered heptene fraction 63. 8 248. 2 80 Aldehyde recovery, vol. percent 95 1 96 10 Total 281. 7 318. 3

EXAMPLE 5 A recovery of 78 percent of the contained heptenes, 1n A i mlxtllre (40 Pement hfiptane and 51 a fraction of 80 percent purity (on an acetonitrile-frce percent heptene), simulating the recovered hydrocarbon basis) was achieved fractions obtained as a by-product from the hydroforrnylation of heptenes to produce octyl alcohols, was prepared by the partial hydrogenation of a sample of heptenes. A mixture of 600 milliliters of the heptene-heptane mixture and 50 milliliters of acetouitrile was fractionally distilled through a packed column. The distillate was condensed and the lower, acetonitrile layer was returned to the column. Distilled fractions and the residue were analyzed for the components and the results are collected in Table Considering fractions 1 through 3 as the waste heptane fraction and the column hold-up and residue as the recovered heptene fraction, a distribution of the components of the sample is presented in Table XI.

It is to be understood that the invention is not to be limited to the exact details of operation shown and described, as obvious modifications and equivalents will be apparent to one skilled in the art, and the invention is, therefore, to be limited only by the scope of the appended claims.

What is claimed is:

1. The method of separating corresponding parafiins and olefins from mixtures comprised of hydrocarbons containing from seven to nine carbon atoms by distilling said mixture with acetonitrile as an azeotrope entrainer and removing the paraffinic fraction as the heterogenous azeotrope from the entrainer.

2. The process of claim 1 where the admixture to be separated is composed of isomeric nonenes and their corresponding isomeric nonanes.

3. The process of claim 1 where the admixture to be separated is composed of isomeric heptenes and their corresponding heptanes.

References Cited in the file of this patent UNITED STATES PATENTS 

1. THE METHOD OF SEPARATING CORRESPONDING PARAFFINS AND OLEFINS FROM MIXTURES COMPRISED OF HYDROCARBONS CONTAINING FROM SEVEN TO NINE CARBON ATOMS BY DISTILLING SAID MIXTURE WITH ACETONITRILE AS AN AZEOTROPE ENTRAINER AND REMOVING THE PARAFFINIC FRACTION AS THE HETEROGENOUS AZEOTROPE FROM THE ENTRAINER. 